Social isolation has considerable effects on human functioning. However, despite the well-established effects of social isolation on physical and mental health, remarkably little is known about the proximal cognitive and neural changes that produce such deleterious outcomes. Studies that have manipulated social isolation report contradictory findings-social isolation can at times increase engagement toward social cues but also diminish engagement with others. The present research aims to reconcile these contradictory findings by testing the hypothesis that social isolation has opposing effects on two different brain systems!one of which leads to hypersensitivity to social stimuli and one of which leads to a reduction in the value associated with social engagement. In doing so, this program of research also makes us of a newly-developed strategy for manipulating social isolation. To date, most researchers have manipulated disconnection as exclusion or ostracism. However, such operationalizations only capture forms of social disconnection that involve rejection, but do not examine an extremely prevalent naturally- occurring form of social isolation: sheer lack of contact with others!social deprivation. To address this shortcoming of earlier research, we will manipulate social isolation as acute social deprivation, in which individuals are actively restricted from contact with others for a relatively long period of time. This operationalization presents an innovation in simulating the common experience of merely being alone rather than being actively rejected by others. The proposed research will use magnetic resonance imaging (MRl) to test the effect of social deprivation on several aspects of social cognition, including th tendency to perceive social cues such as mental states and emotional expressions and the valuation of social rewards. As such, this research aims to shed light on a pervasive cause of isolation that researchers have typically studied only with nonhuman animals (e.g., rats) or in already socially deprived individuals (e.g., prisoners). We propose two experiments that test three specific aims. The first experiment tests the extent to which social deprivation increases social cue detection and mind perception, consequently increasing activation in brain regions associated with social cognition. The second experiment tests the extent to which social deprivation decreases the value associated with social rewards, consequently decreasing activation in brain regions involved in reward processing. In addition, arterial spin labeling and functional connectivity analyses will be administered on brain scans taking during periods of rest during these studies. These methods allow us to test the hypothesis that social deprivation will lead to increased basal metabolic activity and increases the coordinated activity in the brain's default network, a network involved in social cognition.